the 74 had a detuned 350, no big block options

The other numbers stamped on the pad (at least for '65-and-later models) is the engine V.I.N. This nine-character number is normally found beside or under the engine code. Stamped onto the pad by the final assembly plant (where the car is actually built), the number contains a divisional code (1 = Chevrolet), the last digit of the year model and a 1-character code (usually a letter code unless the car was assembled in Canada) for the vehicle assembly plant. Following these three characters are the last six digits of the car serial number (known as the sequence number). The last six digits will match the last six of the car's V.I.N. number if the engine is original.

Sources: yearone.com